The present invention relates to an electric power and cooling system for use on an aircraft.
In addition to propulsion, an aircraft's main engines provide shaft power to drive accessories such as electric generators and pumps, and fresh, pressurized air for the aircraft's environmental control system. This air is used to cool or heat, ventilate, and pressurize the aircraft cabin. The extraction of pressurized air and shaft power from the main engine is referred to as parasitic loss, and must be compensated for by increasing fuel consumption. Not surprisingly, aircraft and engine designers are continuously working on reducing these parasitic losses, and hence reducing the fuel consumption of the main engines.
When the aircraft is on the ground and the main engines are shut down, many aircraft employ an auxiliary power unit. An auxiliary power unit is a small gas turbine engine comprising one or more compressors and a turbine mounted on a shaft. A combustor is disposed between the compressor and the turbine. During operation, the compressor supplies pressurized air to the environmental control system, and the turbine provides shaft horsepower to drive accessories such as an electric generator. Recent technological advances now enable auxiliary power units to start and operate during an in flight emergency such as a main engine shutdown. However, under normal in flight operating conditions, the burden of providing electricity and pressurized air stall falls on the main engines.
One approach to reducing the parasitic losses of the main engines is to combine an auxiliary power unit and an environmental control system into one system and have the auxiliary power unit's compressor continuously provide pressurized air to the environmental control system. Such systems are known in the prior art. Although these systems eliminate the parasitic loss due to the extraction of pressurized air from the main engines, they still require shaft horsepower from the main engines to drive electrical generators. Yet another known approach is to combine an auxiliary power unit and an environmental control system into one system and have the auxiliary power unit drive an electric generator. In such systems however, the auxiliary power unit consumes fuel. Therefore, though the fuel consumption of the main engines is reduced, the overall fuel consumption of the aircraft is not necessarily reduced.
It is also known in the prior art to provide an environmental control system that provides conditioned air to an aircraft's cabin as well as supplying all of the aircraft's electrical needs without an increase of fuel consumption. Such a system is shown in U.S. Pat. No. 5,442,905 to Claeys et al. Despite the existence of such a system, there still remains a need for an environmental control system that can provide both conditioned air and electricity to an aircraft without an increase in fuel consumption.